YOu're looking at a very long flight no matter which airport you choose. 8 hours cramped up can seem like 20-to-life. If you can afford the money, do so. I used to fly to both regularly, and a tight seat sucked. First class is snazzy, but you didn't mention that. Also, British Airway seems to have better seats in general, so you might think of that.

I always found Amsterdam an easy place to move around; London not quite so easy, but that was pre-9/11. I think that the layout is still OK in Amsterdam. Depending on where you are going as your final destination, I vote for Amsterdam. If you're going to Scotland, do the England route and take a train from London. Ha.

Sounds like you have a nice trip lined up in any event.